Photographic silver halide transfer process



1956 E. H. LAND ET AL I 2,774,667

PHOTOGRAPHIC SILVER HALIDE TRANSFER PROCESS Filed July 2, 1951 \PriniReceiving S'I'ra'ium Silver Prccipifafing Layer Subpori V Shipping LayerSilver Prccipiiai'ing Layer aierproof Subcoai [Prini Receiving Sh'aiumSuppor+ FIG. 2

Shipping Layer Abrasion Resisfani Coa'ring Silver Prccipifaflng Layeral'crproof Subcoai {Prim Receiving Sirarum Suppor'i INVENTORS BY 772mm-ATTORNEYS United States Patent 0 PHOTOGRAPHIC SILVER HALIDE TRANSFERPROCESS Application July 2, 1951, Serial No. 234,854

14 Claims. (Cl. 96-29) This invention relates to photographic processesand more particularly to transfer processes wherein a latent image in asilver halide emulsion is developed and a soluble silver complex isobtained by reaction with the undeveloped silver halide of saidemulsion, and wherein the soluble silver complex is transferred fromsaid emulsion to a print-receiving element and the silver thereof isthere precipitated to form a positive print.

One object of the present invention is to provide a novel silver halidetransfer process of the foregoing type, said process being capable ofgiving positive images which are brilliant, which have full-tonegradation, high maximum densities, low minimum densities and homogeneityof hue in highlight and shadow, and whose color range is from blackthrough neutral gray to white.

It is another object to provide a novel transfer process of the abovecharacter which can be performed with a great variety of silver halideemulsions and which is especially suited for giving positive prints oflatent images formed in the very fast negative-type emulsions.

A further object is to provide a transfer process which can be performednot only with a great variety of photosensitive silver halide emulsionsbut also with most of the conventional developing agents andcompositions.

A still further object of the invention is to use in a transfer processan improved print-receiving element comprising a novel silverprecipitating layer adjacent one surface thereof, which layer comprisesa discrete macroscopically continuous film or matrix formed of particlesof colloidal silica in which there is dispersed a silver precipitatingagent. Especially useful for providing the silica of this layer is thesilica dispersion commercially available under the trade name Ludox(Soap and Sanitary Chemicals, volume 25, July issue, pages 121, 123 and125; August issue, pages 115-117) in which the silica micelles areestimated to have a particle size from to 30 millimicrons with anaverage of 15 millimicrons. This dispersion is applied as a layer to asuitable support to provide upon said support the matrix of silica, andcare is taken to retain the silica in its colloidal unprecipitated stateuntil it is so applied to the support. The silica matrix in its solidcondition has dispersed therethrough a silver precipitating agent andthis silver precipitating agent is added to the constituents of thesilica matrix prior to their solidification upon the support.Preferably, the silver precipitating agent is introduced into the silicadispersion prior to its application onto the support or, alternatively,

the silver precipitating agent is added to the layer of and the scope ofthe application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawing wherein:

Figure 1 is a diagrammatic enlarged sectional view illustrating one formof the novel print-receiving element of the present invention;

Fig. 2 is a view similar to Fig. 1 illustrating another embodiment ofthe print-receiving element; and

Fig. 3 is a view similar to Fig. 1 of still another form of theprint-receiving element of the invention.

' It has previously been proposed to employ silver halide transferprocesses otherwise identified as difiusion-transfer reversal processesfor the purpose of forming positive prints upon print-receivingelements. Certain of these proposals have been directed to processes oflimited application suitable essentially for the graphic arts, such asreflex and direct positive printing. These last-mentioned processes areperformed with slow emulsions and in a plurality of steps. They requirea washing or toning operation subsequent to image formation and alsorequire for their performance theimmersion of the photosensitive andprint-receiving elements in baths of the processing agent (A NewPrinciple of Reversal; Reversal-Transfer by Ditfusion by Andre Rott inScience et Industrie Photographique (2) 13: 151-152, July-August 1942,and I. G. F. French Patent No. 879,995).

In the following patent and applications of Edwin H. Land: Patent No.2,543,181, issued February 27, 1951, for Photographic Product Comprisinga Rupturable Container Carrying a Photographic Processing Liquid;applicau'on Serial No. 662,000, filed April 13, 1946, now Patent No.2,584,029, for Photographic Product and Process; application Serial No.726,982, filed February 7, 1947, now Patent No. 2,584,030, forPhotographic Product and Process; application Serial No. 727,382, filedFebruary 8, 1947, now Patent No. 2,698,238, for Photographic Product andProcess; application Serial No. 727,383, filed February 8, 1947, nowPatent No. 2,644,756, for Photographic Product and Process; applicationSerial No. 727,385, filed February 8, 1947, now Patent No. 2,698,245,for Photographic Product and Process; application Serial No. 7,795,filed February 12, 1948, now Patent No. 2,647,056, for PhotographicProcess; application Serial No. 37,252, filed July 6, 1948, now PatentNo. 2,635,048, for Photographic Product and Process; application SerialNo. 88,832, filed April 21, 1949, now Patent No. 2,662,822, forPhotographic Transfer Processes and Products and Compositions for thePractice of said Processes; application Serial No. 164,908, filed May29, 1950, now abandoned, for Photographic Silver Halide Transfer Productand Process; and application Serial No. 176,963, filed August 1, 1950,now abandoned, for Photographic Transfer Processes and Compositions forthe Practice of said Processes; there have been disclosed silver halidetransfer processes capable of (a) operating with fast (negative)emulsions; (b) directly producing stable prints, i. e., prints requiringno washing, toning or other after treatment for their permanency; (c)directly giving positive prints having adequate density, homogeneous huein highlight and shadow and full-tone gradation; (d) operating over aWide range of ambient temperatures; and (e) being performed in a camerawithout baths and with a minute quantity of liquid contained within thefilm. According to the present invention, there is provided an improvedprint-receiving element universally useful in the transfer processesdescribed in the foregoing patents, patent applications and publicationsfor giving prints of improved pictorial quality and colorcharacteristics.

In one of its simplest forms the product of the present inventioncomprises, as shown in Fig. l, a support 13 and a silver precipitatinglayer 15 coated or otherwise applied upon said support. Support 13 maybe formed of almost any rigid or flexible supporting material which ismechanically stable in the presence of conventional photographicdeveloping compositions. For example, for forming positives which are tobe viewed in reflected light, support 13 may be a photographic paperbase, such as baryta paper, and for giving positive transparencies saidsupport may be one of the transparent film bases.

The novel structure of the silver precipitating layer 15 is uniquelyeffective in providing the type of environment required for theformation of positive prints which are brilliant and which havefull-tone gradation, high maximum densities, low minimum densities andhomogeneity of hue in highlight and shadow. Certain of the condi tionswhich must be satisfied in the achievement of such a print have beendescribed in the article entitled One step photography by Edwin H. Landin the Photographic Journal, Section A, January 1950, pages 7 through15. It is there pointed out that the silver precipitating layer must besuitably constituted to build up the deposited silver atoms into arraysof large enough diameter for absorbing visible light and that thesearrays must also have adequate constancy in diameter so that thehighlight and shadow of the positive are of the same hue. Unduemigration or aggregation of the silver precipitants in the silverprecipitating layer will cause silver precipitation to initiate at manypoints so that an enormous number of highly dispersed silver grainsform, thereby diminishing the density of the positive and giving a printwhich has a yellowish hue. For example, colloidal silver dispersions ina protective colloid, such as gelatin, if used as print-receivinglayers, induce precipitation of silver in this highly dispersed form andgive prints having a yellow to light brown color. Attempts to correctthis by the inclusion of conventional blue-black toning agents with thecolloidal silver in the silver precipitating layer are partiallyeffective in giving a more nearly black and white image, but thisimprovement is made at the sacrifice of gradation in density betweenhighlights and shadows. Thus, a product formed in this manner finds itsprincipal application in the graphic arts for document duplication. Adifferent attack upon the problem of silver precipitation which hasresulted in the production of excellent photographic prints suitable forall photographic purposes is represented by the improvements embodied inthe Polaroid Land film. As first made publicly available, this film gavewarm sepia prints. The concepts which have contributed to this advancein the art of forming positive prints by silver halide transfer involvenot only the provision of a proper environment for the precipitation ofsilver but also a closely interrelated chemical environment soconstituted as to avoid the hazards to print stability. In solving thefirst problem so as to obtain prints which have ful-tone gradation andhomogeneity of hue, several important concepts were combined among whichwere the use of lead ions for giving improvements in density and color(application Serial No. 662,000); the use of heavy metal sulfides andselenides in combination with an excess of heavy metal ions capable oftrapping the sulfide ions to confine the latter to their original site(application Serial No. 164,908); and the use of certain inertdispersing media without specific regard to the extent of theirdispersion to provide the initial desirable aggregation of the metallicsulfides or selenides (application Serial No. 7 27,385 These conceptshave provided extremely effective mechanisms for achieving printquality, especially when used in combination.

Another mechanism effective for controlling the silver precipitationduring image formation is the provision of the silver precipitants inthe viscous processing agent rather than in the surface portion of thesolid printreceiving element. These precipitants are provided assubstantially insoluble salts and in a highly dispersed essentiallycolloidal condition (application Serial No.

88,832). This approach tends to precipitate the silver almost entirelyin the layer of processing composition. These mechanisms in speciallyselected combinations are capable of giving prints which not onlypossess the desiderata of a good photographic print, e. g., excellentgradation, homogeneity of hue, high maximum densities and low minimumdensities but are also substantially black and white in color. However,this approach de pends upon the interaction of several components orconcepts for the proper control of the silver precipitation and uponachieving a proper balance between the components. The present inventionprovides a more universal solution to the problem of obtaining highquality, brilliant prints in a color range of from black through neutralgray to white. The product of the present invention tends, whatever thecircumstances, to aggregate the precipitated silver atoms into arrayssuch that the highlight and shadow of the positive are White and black,respectively, and the gradations are neutral gray. These results areachieved by providing as a principal component of the print-receivinglayer a macroscopically continuous film or matrix of silica in whichsuitable silver precipitating agents are dispersed, said matrix beingdeposited from a dispersion in which the silica micelles are present incolloidal form. This dispersion is regarded as either a colloidalsolution of hydrated silica or a polymerized form of siliceous acid insolution. It preferably contains 30% of the silica and also a smallamount of alkali which serves as a stabilizing agent to prevent theprecipitation or gelation of the silica. One available form of thiscolloidal silica is the product sold by Du Pont under the trade nameLudox. In this connection it is to be noted that some equivalency hasbeen observed between silica and other protective colloids inmaintaining colloidal metals in their colloidal condition in liquidsuspensions thereof in a strictly nonphotographic application (Journalof the Washington Academy of Science, volume V, 1915, pages 687l), butfor the purposes herein disclosed, namely, the achievement of a solidmatrix serving as a vehicle for the silver precipitating agent and forreceiving and precipitating silver, there is a vast and dramaticdifference between the functioning of silica and other suspending anddispersing media and also between silica in this hydrated and colloidalcondition and silica in its other states of aggregation.

The silver precipitating agents are preferably introduced into thesilica dispersion prior to its application to the support 13 and inquantities and under such conditions as to clearly preclude any gelationor precipitation of the silica of the dispersion. Preferred as silverprecipitating agents are the metallic sulfides, selenides andselenosulfides, these terms being understood to include the polysulfidesand polyse'lenides. Also suitable as precipitants are such colloidalmetals as silver, gold and mercury, provided that the same areintroduced into the silica matrix in intimate mixture with a protectivecolloid capable of preserving their colloidal state. The amounts ofprotective colloid necessary for this purpose are relatively trivial incomparison to the mass of the silica of the matrix so that the essentialphysical and chemical characteristics of the matrix are not appreciablymodified by the presence of the protective colloid. Still othersatisfactory silver precipitating agents are .dithioox-amate and itslead and zinc complexes, potassium dit-hiooxalate and the lead complexesthereof and thioacetamide.

The combination of a silver precipitating agent and a discretemacroscopically continuous matrix of silica thus provides an environmentin which the silver atoms will deposit in aggregates having high enoughconductivity and large enough diameter to be black, like these orordinary positive paper, without requiring any special reagents forconfining the silver precipitant to its original site. The use of suchreagents may, however, assist in increasing the density and improvingthe stability of the positive print. The novel precipitating layer .soprecipitates and aggregates the silver as to give it a very highcovering power in the order of five times that of the silvenin thenegative. 1

One example of a process for forming print-receiving elements comprisinga support 13 and a silver precipitating layer 15 is the following:

EXAMPLE 1] A solution is formed by mixing together:

A precipitate is obtained which-is thereafter dissolved by being washedin 3 cc. of a solution of ammonium hydroxide (NH4OH).

. This solution is then added to 100 cc. of a 2% gelatin solution andthe mixture ,is heated in a water bath and after heating is permitted tostand for approximately fifteen hours. The solution is then evaporatedin an evaporating dish and the dry residue is redissolved in 20 cc. ofwater. 3.6 cc. of the resulting solution are added to 300 'cc. of Ludoxand the mixture thus formed is applied as a coating to a support 13.

'Afurther type of silver precipitating agent which is usefulis 'the'silver-protein composition synthesized in accordance with the procedureoutlined in Dansk. Tids. Farm. 18, pages 53 to 83, 1944, and asatisfactory coating composition for layer 15 is one formed from amixture of 400 cc. of Ludox and 1.58 grams of said silver-proteincomposition. 1 Y

A positive sheet so constructed may be employed ina process similartothat described in my above-mentioned copending application Serial No.7,795, with a processing composition comprising:

Water cc 398 Sodium carboxymethyl cellulose (high viscosity) grams 15225Sodium sulfite do 25.6 Sodium hydroxides. do 15.2 Sodium thiosulfate do5.4 Hyd'roquinone d O 52 6-nitrobenzimidazole do .5 Metol do .5

The print-receiving elements of the present invention may be suitablyemployed to form transfer prints when used with a great variety ofphotosensitive emulsions. For example, satisfactory results can be hadwith any of the following films: a

Eastman films Photoflure (PF-470) 'Verichrome Plus-X (rolls and packs)Super-XX (rolls and packs) Plus-X (35 mm. 7 and bantam) Panatomic-X VSuper-XX (35 mm. and bantam) Fine Grain Positive High Contrast PositiveMicro-File Super, Panchro-Press, Sports Type T ri-X Super Panchro-Press,Type B Super-XX (sheet films) Portrait Panchromatic Panatomic-X Ortho-X.

Super Ortho-Press Super Speed Ortho'Portrait Commercial Infrared Tri-XAero f Super-XX Aero Infrared Aero -6 Contrast Process'Ortho 7 ContrastProcess Pan Kodabromide Royal Bromide Eastman Background X I v Anscofilms Plenachrome '7 Superpan Press Triple S Pan Isopan Triple S OrthoCommercial Ortho Defender films Arrow Pan Fine Grain Pan XF PanchromaticDu Pom films High Speed Pan Type 428 High Speed Varigam Photowrit KArrow Pan Varigam R XF Pan A great variety of silver halide developersmay be used inthe processing composition which participates in theformation of the transfer print. For example, any of the followingdevelopers may be satisfactorily employed:

. For certain purposes, especially when a viscous processing compositionis to be used and spread over the surfaceof :the print-receiving elementduring the performance of the process, it is desirable to so constructthe print-receiving element as to confine the permeability thereof to a.very thin surface stratum and also to so construct the surface of theelement that the viscous continuum of theprocessing compositionseparates therefrom and leaves no droplets or film of developingcomposition on'the print-receiving layer. As a result of thisconstruction, prints are obtained which are dry immediately uponseparation from the photosensitive element and which do not curl-ordistort as a result of changes in atmospheric conditions. Also, as aresult of this construction, such .of the stain-forming reactants as areretained by the printreceiving element after the formation of thepositive print are primarily confined to the thin print-receivingstratum. Because the print-receiving stratum constitutes such a smallproportion of the total thickness of the material permeated by theliquid, there is, in effect, a lesser mass of these undesirablestain-forming reactants in the printreceiving element than would existif a greater thickness of said element were penetrated by the liquidprocessing agent.

One embodiment of this type of print-receiving element is illustrated inFig. 2 and, as shown, comprises a suit able support 13 and aprint-receiving stratum 15, the latter in turn comprising a strippinglayer 15a, preferably .of from l'to 3 microns in thickness, whichconstitutes the .outer' surface portion thereof and a silverprecipitating layer 15b, also preferably of from 1 to 3 microns inthickness. Between the print-receiving stratum 15 and the support 13there is a water-impermeable layeror subcoat 16. Support 13 may beformed of a water-permeable material, such as an uncoated orgelatin-coated paper or of a substantially water-impermeable material,such as a cellulose ester, fonexaniple, cellulose nitrate, celluloseacetate "7 separate film of one of the water-impermeable materials andis coated on said support in sufficient thickness to prevent anyappreciable penetration of the liquid therein during the transferprocess. If support 13 is substantially water impermeable, layer 16 maybe just an integral extension of said support.

It is to be noted also, in connection with water-impervious layer 16,that its primary purpose is to prevent any substantial penetration ofthe liquid processing agent beyond print-receving stratum 15 during theperformance of the transfer process and that in general the process forforming the positive print takes less than five minutes for itscompletion and more usually only about one minute. Accordingly, thewater impermeability of layer 16 need only be such as will prevent anypenetration of an aqueous liquid therethrough during this time, and theterm water-impermeable, as used hereinafter, in connection with layer16, is to be understood as pertaining to an impermeability of thisorder. It may be desirable in some instances to provide layer 16 with afurther thin subcoat (not shown) for improving the adhesion betweenlayer 16 and stratum 15.

Stripping layer 15a minimizes the adhesion between the essentially solidresidual film, formed when a viscous processing agent is used, and theprint-receiving element so that upon separation of the print-receivingand photosensitive elements the solid residual film will adhere to thephotosensitive element and will be stripped therewith from theprint-receiving element.

Examples of a print-receiving element comprising a thin print-receivingstratum and capable of being stripped from the solid residue of aviscous processing composition are the following:

EXAMPLE 2 There is applied, as by roll coating, on the barytacoatedsurface of a baryta paper 13, a solution consisting of:

Polyvinyl butyral (unplasticized) grams 35 Isopropyl acetate cc 525Methanol cc 175 to provide said support 13 with a subcoat 16 of thepolyvinyl butyral thick enough to be water impermeable.

A solution A is formed by mixing together:

Lead acetate "grams" 0.21 Cadmium acetate do 2.28 Zinc acetate do 3.80Water cc 100.0

A solution B is made by mixing 100 grams of sodium sulfide in 100 cc. ofwater, adding thereto 90 grams of powdered selenium and then addingwater to make 1000 cc. A coating composition is then formed comprising:

Solution A cc 10.0 Ludox cc 400.0 Sodium hydroxide grams .3 Solution Bcc 15.0

This composition is then applied, as by roll coating, upon the subcoat16 and forms the further layer 15b. The composition is roll-coated in athickness which gives a layer 15b approximately 2 to 3 microns thick. Toexpedite the application of this layer 15b upon subcoat 16, a smallquantity of wetting agent may be added to the composition. Thereafter,stripping layer 15a is formed on the surface of silver precipitatinglayer 15b by roll coating thereon against a smooth surface, such forexample as the polished surface of a metal drum, a aqueous solution ofpolyvinyl alcohol in a layer which gives a polyvinyl alcohol coating ofa thickness of approximately one to two and one-half microns.

It is to be noted that thecoating composition which provides layer 1512contains but a small proportion of solid reagents other than thecolloidal silicamicelles and includes a sufficient amount of sodiumhydroxide to maintain the silica particles in their colloidal state.

EXAMPLE 3 For the coating composition which provides the silverprecipitating layer 15b of Example 2 there is substituted a compositioncomprising the following:

Ludox 300.0 Solution B of Example 2 22.4 .025 molar solution of leadnitrate 13.6

EXAMPLE 4 For the coating composition which provides the silverprecipitating layer 15b of Example 2 there is substituted a compositioncomprising the following:

Cc. Ludox 200.0 Solution B of Example 2 40.0

EXAMPLE 5 For the coating composition which provides the silverprecipitating layer 15b of Example 2 there is substituted a compositioncomprising the following:

Cc. Ludox 300.0 Solution B of Example 2 5.6 .05 molar solution ofleadnitrate 13.6

Waterproof subcoat 16 may, for example, be formed of such othermaterials as cellulose nitrate, cellulose acetate, cellulose butyrate orcellulose acetate propionate. Stripping layer 15a may be, for example,gum arabic, cellulose acetate-hydrogen phthalate, polyvinyl alcohol,hydroxyethyl cellulose, sodium alginate, pectin or polymethacrylic acid.Layer 15a may also be formed of such less permeable materials as methylcellulose, ethyl cellulose and certain of the methacrylic esters, but inthe latter case it is preferably very thin, having a thickness of fromone to three microns.

The products of the present invention are especially well suited for theformation of substantially grainless positive transparencies which arecapable of being enlarged by projection to a substantial extent withoutappreciable loss in definition. A print-receiving element capable ofgiving positive transparencies is formed by coating upon a transparentsupport of cellulose acetate one of the silver precipitating layers 15or 15b of the above-noted examples.

In another embodiment of the print-receiving element, as shown in Fig.3, a layer is provided between stripping layer 15a and silverprecipitating layer 15b, said layer 150 serving to improve the abrasionresistance of the silver precipitating layer and also to minimize theionic penetration into layer 15b of certain of the stainformingcomponents of the processing composition. Very satisfactory results areobtained with this arrangement when stripping layer 15a is selected fromsuch of the materials noted above as being suitable for the strippinglayer as are relatively soluble in an aqueous alkaline solution andlayer 150 is a less soluble, although relatively permeable, material.For example, satisfactory results have been obtained by formingstripping layer 15a from gum arabic and abrasion-resistant layer 15cfrom polyvinyl alcohol. Similar satisfactory results may be obtained byusing two polymeric materials Whose chemical structures are the same butwhose molecular weights differ. For example, a low molecular weightpolyvinyl alcohol could be used as stripping layer 15a whereas asubstantially higher molecular weight polyvinyl alcohol would besatisfactory in this case as abrasion-resistant layer 150. Also usefulare mixtures of the same materials in different concentrations. Forexample, both layers may be formed from mixtures of gum arabic andpolyvinyl alcohol with layer 150 comprising a substantially higherconcentration of polyvinyl alcohol than layer 15a.

A modification of the print-receiving element of Figs. 2 and 3 isobtained by applying a thin silver precipitating layer 15b, for exampleof from 1 to 3 microns in thickness, on the subcoated or otherwisewater-impervious support '13 and omitting the abrasion-resistant coatingand the stripping layer. This type of sheet is particularly useful withemulsions which are relatively thick and in processes wherein theprocessing composition is spread in a very thin viscous film between thephotosensitive emulsion and the print-receiving element. When theprint-receiving element is so processed and is thereafter separated fromthe photosensitive element, the plastic content of the processingcomposition strips with the print-receiving element and provides thereona thin protective film. Be-

cause of the thinness of this residual plastic layer and of theprint-receiving layer, especially as compared to the thickness of theemulsion of the photosensitive element, essentially all of thestain-forming components of the process are carried away with thephotosensitive emulsion.

As noted previously, one of the important features of theprint-receiving elements herein described is their general usefulnesswith a great variety of photographic emulsions and developingcompositions and also in the various known types of silver halidetransfer processes. A satisfactory process for using theseprint-receiving elements and one which is generally preferred, becauseof its inherent advantages, is the process disclosed in the abovenotedcopending application Serial No. 7,795 and the elements are alsoespecially adapted for use in composite structures of the type shown inthe aforementioned Patent No. 2,543,181. However, they may also besuccessfully employed in processes involving a plurality of steps andwhich require conventional baths of reagents for their performance. Inorder to make the print'receiving elements especially suited to thelatter type of process, it is desirable to include as part of thestructure of said elements a suitable silver halide solvent. Forexample, a water-soluble thiosulfate or thiocyanate salt may be used,such as lead thiosulfate. Such a salt may be dispersed throughout thesurface portion of the print-receiving element so as to be readilyaccessible for dissolution in any liquid which permeates said surfaceportion.

One example of a print-receiving element which incorporates a silverhalide solvent is obtained as follows:

EXAMPLE 6 On the print-receiving element of Examples 2 through athiosulfate containing layer is formed by roll coating thereon thefollowing composition:

Using a print-receiving element of this type, it becomes possible withany conventional type of silver halide emulsion to form a positive printof a latent negative image in said emulsion by means of standard silverhalide developing compositions. The exposed photosensitive emulsion isimmersed in a bath of the developing composition to develop the latentimage therein and is thereafter removed from the bath and pressed intoengagement with the print-receiving element. The wet photosensitiveelement provides the necessary liquid for dissolving the silver halidesolvent from the print-receiving element and for making the solventavailable for forming a soluble silver complex with the unexposed silverhalide of the photosensitive element. This complex is transferred to thesilver precipitating layer and the silver thereof is there precipitatedto form the positive print. This same type of print-receiving elementcan also he satisfactorily employed when the processing is performed bymeans of a viscous processing composition spread between thephotosensitive element and the print-receiving element and without anyinterven ng liquid treatments of the photosensitive element. In thelatter case, the silver halide solvent ordinarily initially present inthe viscous liquid processing composition may be omitted. When leadthiosulfate in the print-receiving element is the source of the silverhalide solvent, it is preferable that the developer composition have ahigh pH;

It is to be understood, of course, that either of the compositions whichmay be coated in accordance with Example 1 to provide silverprecipitating layer 15 of the structure of Fig. 1 may be suitablysubstituted for the coating compositions which provide the silverprecipitating layer 15b of the structures of Figs. 2 and 3.

Since certain changes may be made in the above process without departingfrom the scope of the invention herein involved, it is intended that allmatter contained in the above description or shown in the accompanyingdrawing shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:

l. The process of forming images in silver which comprises developing alatent image in a silver halide emulsion, reacting a silver halidesolvent with part at least of the undeveloped silver halide of saidemulsion, transferring at least part of said soluble silver complex toan image-receiving material comprising a silver precipitating agentdispersed in a silica matrix formed by the hardening in situ of acolloidal solution of hydrated silica whose silica particles have aparticle size averaging less than 30 millimicrons, and precipitating thesilver of said complex at said image-receiving material to form a printof said latent image among said hydrated silica.

2. The process of claim 1 wherein the silver precipitating agent is fromthe class consisting of the sulfides, selenides and selenosulfides.

3. The process of claim 1 wherein the silver precipitating agent is acolloidal metal.

4. The process of claim 3 wherein the colloidal metal is a noble metal.

15. The process of claim 3 wherein the colloidal metal is $1 ver.

6. The process of claim 1 wherein the silver precipitating agent is asilver salt.

7. The process of claim 1 wherein the image-receiving material is in theform of a print-receiving layer and is provided on a support.

8. The process of claim 7 wherein the silver precipitating agent iscolloidally dispersed among the hydrated silica of the matrix.

9. The process of claim 8 wherein the surface portion of said supportupon which said print-receiving layer is mounted is substantially liquidimpervious.

10. The process of claim 9 wherein said print-receiving layer has athickness less than approximately 3 micron-s.

11. The process of claim 1 wherein the image-receiving material is inthe form of a print-receiving layer supported by paper.

12. The process of claim 1 wherein the image-receiving material is inthe form of a print-receiving layer supported by a transparent filmbase.

13. The process of claim 1 wherein the silica particles have an averageparticle size of approximately 15 millimlCIOIlS.

14. The process of claim 7 wherein the silica particles have an averageparticle size of approximately 15 millimicrons.

References Cited in the file of this patent UNITED STATES PATENTS1,355,299 Bender Oct. 12, 1920 1,547,236 Reyerson July 28, 19251,701,075 Jaeger et a1 Feb. 5, 1929 (Other references on following page)UNITED STATES PATENTS FOREIGN PATENTS 1,882,146 Holmes Oct. 11, 193253,502 Fran-0e July 16, 1945 2,352,014 Rott June 20, 1944 59,365 HollandApr. 17, 1947 2,399,981 Britt May 7, 1946 2,424,083 Finch et a1. July15, 1947 5 OTHER REFERENCES 2 433 515 Jahoda 13 30 1947 Garnen:Photographic Notes, v01. 6, October 1861, 2,626,867 Webster Jan. 27,1953 P 2 93 237 d 23 1954 Bur-mistrov: The Photographic Journal, August1936, 2,698,245 Land Dec. 28, 1954 Pages 452-459 2,699,393 Weyde Ian.11, 1955 10

1. THE PROCESS FOR FORMING IMAGES IN SILVER WHICH COMPRISES DEVELOPING ALATENT IMAGE IN A SILVER HALIDE EMULSION, REACTING A SILVER HALIDESOLVENT WITH PART AT LEAST OF THE UNDEVELOPED SILVER HALIDE OF SAIDEMULSION, TRANSFERRING AT LEAST PART OF SAID SOLUBLE SILVER COMPLEX TOAN IMAGE-RECEIVING MATERIAL COMPRISING A SILVER PRECIPITATING AGENTDISPERSED IN A SILICA MATRIX FORMED BY THE HARDENING IN SITU OF ACOLLOIDAL SOLUTION OF HYDRATED SILICA WHOSE SILICA PARTICLES HAVE APARTICLE SIZE AVERAGING LESS THAN 30 MILLIMICRONS, AND PRECIPITATING THESILVER OF SAID COMPLEX AT SAID IMAGE-RECEIVING MATERIAL TO FORM A PRINTOF SAID LATENT IMAGE AMONG SAID HYDRATED SILICA.